1. Field of the Invention
The present invention relates to the field of downhole fluid analysis in hydrocarbon producing wells for determining fluid density, viscosity, and other parameters for a fluid downhole in a borehole during production, monitoring while drilling or wire line operations.
2. Background Information
Oil and gas companies spend large sums of money to find hydrocarbon deposits. Oil companies drill exploration wells in their most promising prospects and use these exploration wells, not only to determine whether hydrocarbons are present but also to determine the properties of those hydrocarbons, which are present.
To determine hydrocarbon properties, oil and gas companies often withdraw some hydrocarbons from the well. Wireline formation testers can be lowered into the well for this purpose. Initially, fluids that are withdrawn may be highly contaminated by filtrates of the fluids (“muds”) that were used during drilling. To obtain samples that are sufficiently clean (usually <10% contamination) so that the sample will provide meaningful lab data concerning the formation, formation fluids are generally pumped from the wellbore for 30-90 minutes, while clean up is being monitored in real time. Then, these withdrawn fluids can be collected downhole in tanks for subsequent analysis in a laboratory at the surface.
Alternatively, for some properties, samples can be analyzed downhole in real time. The present invention relates both to monitoring sample clean up and to performing downhole analysis of samples at reservoir conditions of temperature and pressure. A downhole environment is a difficult one in which to operate a sensor. Measuring instruments in the downhole environment must operate under extreme conditions and limited space within a tool's pressure housing, including elevated temperatures, extreme vibration, and shock.